The present invention relates to an eye-examining instrument in general, and more particularly to an instrument by means of which the shape of the cornea of the eye can be determined.
In many instances, it is necessary to determine the corneal radius of an eye, usually in more than one plane. One of these instances, possibly the most important one but not the only one, is encountered in the making or fitting of hard or soft contact lenses where the concave surface of the respective contact lens will have to conform, to the largest feasible extent, to the shape of the outer surface of the cornea to obtain a good fit which will not only reduce if not eliminate any discomfort perceived by the wearer of the contact lens, but will also minimize the possibility that air inclusions or bubbles could be trapped between the external surface of the cornea and the concave surface of the contact lens.
The need for making this determination and taking the appropriate measurements has been recognized a long time ago and various instruments have been proposed for accomplishing this purpose. So, for instance, the U.S. Pat. No. 3,797,921, issued on Mar. 19, 1974, discloses a photographing apparatus for determining corneal radius. This apparatus has substantial dimensions so that it has to be stationarily mounted on a support in an examination room. This apparatus has a generally tubular casing which, at its end facing the patient, carries a part-spherical focusing screen having a plurality of transparent circles thereon. Light from a source located within the casing passes through the transparent circles onto the cornea being examined to form a plurality of ring-shaped images on the cornea. These images are then photographed by a camera located at the end of the casing which is remote from the focusing screen, through a tubular element passing through the center of the focusing screen. Besides being bulky and hence usable only in the examination room setting, this apparatus is also disadvantageous in that the light from the light source is unevenly distributed between the individual transparent circles as well as within each circle, which renders a proper evaluation of the photograph of the cornea and the images of the circles formed thereon difficult. Also, in the event that the cornea is aspherical, that is, when it has different radii of curvature in different planes including and intersecting the axis of the apparatus and the coincident axis of the cornea, it is very difficult to establish the degree and orientation of the asphericity, especially when the variations in the radius of curvature are quite small.
This latter problem is avoided, at least to a certain degree, in the apparatus disclosed in the U.S. Pat. No. 4,046,463, granted on Sept. 6, 1977, wherein a plurality of lamps is provided at the end of the apparatus which faces the patient, the lamps being uniformly distributed on a circle centered on the axis of the apparatus. Thus, an individual image of each of the lamps is formed on the cornea of the eye being examined and the radii of curvature of the cornea in various planes can be determined by measuring the distance between the images which are located diametrically opposite in the respective plane. Here again, the apparatus is very bulky and thus suitable for use only in the environment of an examination room. Furthermore, the rather intense light emitted by the lamps inconveniences the person being examined and may even cause some involuntary eyelid movements which then would interfere with the proper examination. In addition thereto, the provision of the lights on just a single circle does not permit a thorough examination of the cornea and all its possible peculiarities.